In the hydrometallurgical industry, it is of common practice to refine metal by electrolysis in electrolytic cells especially designed for this purpose. The metals to be refined are usually conventional metals such as copper, zinc, nickel or cadmium, or precious metals such as silver, platinum or gold, and others.
It is also of common practice to use metal plates as anodes or cathodes or both. These metal plates often weight several hundred pounds. Usually, the metal to be refined, or the metal used to carry the electric current, is in the form of plates of a given thickness, which are provided at their upper end with two laterally extending projections, called hanging legs. Such projections facilitate gripping, handling and hanging of the plates on lateral sidewalls of the cells. These projections also serve to electrically contact or insulate the electrode.
In use, the electrode plates which, as mentioned, can each weigh several hundred pounds, are immersed into the cells in parallel relationship and are used as anodes, cathodes or both, depending on the affinity of the metal being refined.
In order to have the electrodes positioned in a precise desired location, it is of common practice to place a component called a “capping board” or a “bus bar insulator” onto the top surface of each lateral sidewall of the cells. These capping boards are used to position the plates with respect to each other. They are also used as electric insulators between adjacent cells and/or the electrodes and/or the ground.
In practice, the capping boards are used not only as supports to position the electrodes, but also as supports to avoid damage to the masonry, concrete or polymer-concrete forming the lateral side walls of the cells during the insertion and removal of the heaving electrodes. They are also used for electrolytic refining and electro-winning of metals.
Capping boards are further used in combination with electrically conductive “contact bars”, the purpose of which is to allow electrical connection between the ends of the anodes and cathodes located in adjacent cells. Thus, the combined use of capping boards and contact bars allows both insulation and distribution of electric current.
To achieve proper electrical contact with the contact bar, the plates forming the electrodes are provided with support hanging legs externally projecting on their opposite upper ends. Only one end of the legs of each plate is in contact with a contact bar on one side of the cell where it is located. The other leg of the same plate is held onto the capping board located on the opposite side of the cell in such a way as to be electrically insulated. Thus, the capping board per se plays the role of an insulator and is thus made of insulating material. The contact bar usually extends over the full length of the corresponding capping board in order to connect altogether all the anodes of one cell to all the cathodes of the adjacent cell and vice versa. The contact bar may interconnect all of the cathodes to the anodes on other adjacent cells or perform other electric connection function between electrodes as desired.
Additionally, capping boards may be designed to receive one or more contact bars arranged in a parallel relationship. For example, a capping board may be provided with a primary contact bar and a secondary contact. The primary contact bar may contact anodes and the secondary contact bar may contact cathodes, or vice-versa. Electrolytic cells including three or more contact bars may also be used in electrolytic refinery of metals, such as described in patent documents U.S. Pat. Nos. 8,308,920, 6,342,136 and CA 1.201.681.
In hydrometallurgical refining of metals, during recovery of the metal (such as copper), some of the cathodes are removed from the corresponding contact bar to recover the metal that has accumulated thereon. So as to keep the electrolytic cell refining the metal, one cathode over three cathodes are usually removed from the contact bar (more rarely, one cathode over two are removed from the contact bar). The removal of a portion of the cathodes from the contact bar may cause electric short-circuits. Short-circuits may also be caused by many other factors, such that some major metal refineries may suffer from about 5,000 short-circuits per day.
So far, it has been of common practice to use contact bars made as a one piece structure extending over the full length of the electrolytic cell. However, advantageously the contact bar may be segmented into a plurality of contact bar segments as disclosed in U.S. 61/751,501. The contact bar segments may have various configurations and numbers of contact with cathodes and anodes.
There is a need for improved solutions enabling improved current density distribution along the length of the electrolytic cell and reduction of the short-circuit risks during metal refining and recovery.